Except Craig wasn't always better than Janaszak at the collage level and that's all Herb would of had to go on now wouldn't he.
Craig did play much better than Janaszak at times but he also played much worse.
... The U.S. national team played a ton of games before the Olympics started. Brooks had more than enough time to see both goalies playing behind the same team. The national team played at least 65 games - nearly a full NHL season of games - far more games than a typical college team would play in a season.
Craig was definitely the more consistent goalie game to game during that period of time. Janaszak had a couple of shutouts, but also had games where he was lit up; he was not the steady goaltender of the two, in fact
Steve was the streaky one. If Janaszak had clearly out-played Craig during this time, Janaszak would have been the starter in the Olympics.
The scene in "Miracle" when Herb tells Craig that he's going to go with Janaszak because he doesn't feel Jim "has it" was not made up.
... Brooks liked to use generalities and vagaries so that A) he wouldn't have to reveal his true reasons for doing what he did, and B) it helped him to keep his players (and his assistant coach) on edge, which was how he preferred to coach. It also helped him as a storyteller later on.
Like I said, Brooks had more than enough time to look at both goalies before he made his decision on who would be the #1 at Lake Placid. Brooks also knew that Craig had played on the WEC-A All-Star team for the U.S. a year earlier, and had played pretty well. Before that, Craig had a 29-4-2 record for Boston U. (including a 16-0-0 season as a 20-year-old), and you can bet that Brooks was well aware of that as well.
The two goalies were somewhat close, but Craig was clearly the choice to be his number one. Brooks wasn't stupid. He knew what he had going in, he had a lot of time to see both goalies in action first-hand, and he rightly and logically went with the better man.